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Bureau of Mines Information Circular/1987 



Surface Testing and Evaluation 
of the Monorail Bridge Conveyor 
System 



By Robert J. Evans, William D. Mayercheck, 
and Joseph L. Saliunas 




UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 9146 



Surface Testing and Evaluation 
of the Monorail Bridge Conveyor 
System 



By Robert J. Evans, William D. Mayercheck, 
and Joseph L. Saliunas 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 



Library of Congress Cataloging in Publication Data: 







Evans, Robert J. 

Surface testing and evaluation of the monorail bridge conveyor 
system. 

(Information circular ; 9146) 

Bibliography. 

Supt. of Docs, no.: 1 28.27: 9146. 

1. Mining machinery -Testing. 2. Monorail conveyors -Testing. 1. Mayercheck. William L). 
II. Saliunas, Joseph L. III. Title. IV. Series: Information circular (United States. Bureau of 
Mines) ; 9146. 



TN295.U4 [TN345] 



622 s 



[622'.66] 



86-600401 



CONTENTS 

Page 

Abstract 

Introduction 

Background 

Description of monorail bridge conveyor system 3 

Conveyor units • • 

Power and control 5 

Tramming and support system 8 

Inby support 9 

Outby support 9 

Surface testing 10 

Test rig installation 10 

Initial checkout 11 

Power consumption 12 

Disabled brake test 14 

Haulage rate 14 

Miner loading trials 16 

Reliability 17 

System compatibility with low-belt structure 20 

Suspension of monorail track by chain hangers 20 

System compatibility with hopper-feeder 22 

Summary of surface test findings 22 

Modifications 22 

Mining plans 24 

Conclusions 31 

Appendix A. — Modifications to the monorail bridge conveyor system 32 

ILLUSTRATIONS 

1. Three types of monorail bridge conveyor units 3 

2. Plan view of monorail bridge conveyor unit 5 

3. Intermediate unit 6 

4. Inby unit 6 

5. Outby control boxes 7 

6. Pendant control 7 

7. Monorail T-section track configurations 8 

8. Monorail hardware 9 

9. Outby support with dolly 10 

10. Surface test rig 11 

11. Monorail bridge conveyor system in test rig 11 

12. Typical power-consumption plots 14 

13. Closed-loop configuration 14 

14. Monorail bridge conveyor units at maximum-angle relationship 15 

15. Haulage-rate plot 16 

16. Haulage-rate and power plots during maximum haulage-rate trial 16 

17. Continuous miner loading directly into monorail bridge conveyor 17 

18. Loading rate and power consumption during reliability trial 18 

19. Spillage under inby monorail bridge conveyor transfer point 19 

20. Profile of chain-suspended monorail track 21 

21. Chain hanger 21 

22. Hopper-feeder-bolter 23 

23. Hopper-feeder-bolter compatibility trial 23 



11 



ILLUSTRATIONS— Continued 



Page 



24. 
25. 
26. 
27, 
28. 
29. 
30. 
31. 
32, 
33. 
34. 
35. 
36. 



Monorail installation with chain hangers , 

Monorail installation with roof plates over low-belt structure. 

Monorail bridge conveyor track turnout plans , 

Five-entry mine plan 

Five-entry 60° mine plan with rooms , 

Seven-entry mine plan , 

Mine plan for longwall panel-entry development , 

Monorail bridge conveyor used with shortwall mining system...., 

Monorail bridge conveyor with continuous miner , 

Hopper-feeder-bolter , 

Monorail bridge conveyor used with hopper-feeder , 

Monorail bridge conveyor-hopper-feeder interface , 

Monorail track, installation plan , 

TABLES 

Monorail bridge conveyor specifications , 

Monorail bridge conveyor power consumption , 



24 
25 
25 
26 
27 
27 
28 
28 
29 
29 
30 
30 
31 



4 
13 





UNIT OF MEASURE 


ABBREVIATIONS USED 


IN THIS REPORT 


ft 


foot 


lb/ft 


pound per foot 


ff lb 


foot pound 


min 


minute 


ft/min 


foot per minute 


pet 


percent 


h 


hour 


r/min 


revolution per minute 


hp 


horsepower 


s 


second 


Hz 


hertz 


St 


short ton 


in 


inch 


st/h 


short ton per hour 


in/ft 


inch per foot 


V ac 


volt, alternating current 


kW 


kilowatt 


V dc 


volt, direct current 


lb 


pound 


W 


watt 



SURFACE TESTING AND EVALUATION OF THE MONORAIL BRIDGE 

CONVEYOR SYSTEM 

By Robert J. Evans, 1 William D. Mayercheck, 2 and Joseph L. Saliunas 3 



ABSTRACT 

The monorail bridge conveyor (MBC) is a prototype continuous face 
haulage system that was surface tested and evaluated by the Bureau of 
Mines. The MBC consists of a series of cascading belt bridge conveyors 
suspended from roof-supported monorail track. Tests were conducted to 
determine MBC haulage capability, maneuverability, power consumption, 
and reliability using rigid and chain-suspended monorail track installa- 
tions. Subsequent modifications to improve operation and reliability 
made during surface testing are described. Mining plans were devised 
to show potential MBC installations for room-and-pillar, longwall devel- 
opment, and shortwall mining sections. Compatibility tests were con- 
ducted with the Bureau's prototype hopper-feeder, to provide additional 
surge capacity and lump-breaking capability. Results from the surface 
test program, along with modifications to improve system operation and 
reliability, indicate that the MBC has the potential to perform success- 
fully in an in-mine trial. 

'Civil engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
Supervisory physical scientist, Pittsburgh Research Center. 
3 Project engineer, Boeing Services International, Pittsburgh, PA. 



INTRODUCTION 



The Bureau of Mines has sponsored nu- 
merous high-risk research programs over 
the past decade to improve productivity 
and health and safety in underground coal 
raining by advancing state-of-the-art con- 
tinuous face haulage systems. These sys- 
tems are designed to move coal nonstop 
from the continuous miner to the next 
stage of rail or belt haulage (approxi- 
mately 500 ft). One of the more innova- 
tive continuous face haulage systems is 
the monorail bridge conveyor (MBC). The 
MBC consists of a series of cascading 
belt conveyors supported by an inverted 
T-section monorail bolted to the mine 
roof. The basic concept was conceived 
and patented by the Bureau in 1979 (U.S. 
Pat. 4,157,757). It was designed and 
fabricated by the Goodman Conveyor Co. , 
Inc. under a cost-sharing arrangement 



with the Bureau (contract J0333917). 
This system has the potential to improve 
productivity over conventional shuttle- 
car haulage systems by eliminating 
shuttle-car change, which can amount to 
10 pet of the total face time for a con- 
tinuous miner per shift; it provides a 
captive guidance system that requires 
only one operator, regardless of length; 
and it allows haulage in poor bottom con- 
ditions where conventional rubber tired 
and cat systems could not operate effi- 
ciently. Two of the MBC safety features 
are elimination of potential shuttle-car 
trailing cable and moving-vehicle acci- 
dents. MBC applications include all 
room-and-pillar operations such as driv- 
ing rooms, entries and panels, pillar ex- 
traction, and shortwall mining. 



BACKGROUND 



Underground continuous haulage systems 
have been employed in Europe and the 
United States since 1970. Commercially 
available systems can be grouped into 
three general categories: (1) crawler- 
mounted alternating series of mobile 
bridge carriers and piggyback bridge con- 
veyors, and (2) monorail suspended sys- 
tems, and (3) noncascading systems. The 
crawler-mounted systems generally require 
an operator every 50 ft and are limited 
to a total length of under 200 ft. 

The only commercial monorail system 
available today has been installed in a 
U.S. trona mine and at several foreign 
locations. Although it has a unique con- 
tinuous belt with no crossover points, it 
is relatively heavier and more expensive, 
and it is more difficult to change the 
system length in comparison with the MBC 
system, which can attain a length of more 
than 500 ft with just a single operator. 

The noncascading systems, which have 
been recently introduced and remain un- 
tested underground, are relatively more 
expensive and present more difficulties 
in changing the system length. 

Extensive surface testing and evalu- 
ation of the MBC was conducted by the 
Bureau. The objectives of the surface 
test and evaluation program were to — 



1. Rigorously test the MBC and improve 
performance, based upon observations made 
under simulated underground operation; 

2. Measure MBC performance criteria so 
that underground performance and operat- 
ing requirements could be predicted; 

3. Determine if the MBC meets its de- 
sign criteria and is worthy of an in-mine 
trial; and 

4. Prepare the MBC for an in-mine 
trial including electrical approval by 
the Mine Safety and Health Administration 
(MSHA). 

The principal advantages of surface 
testing, prior to an in-mine trial, are 
that equipment performance can be proven, 
and improved upon, without interfering 
with production at an operating mine. 
This is absolutely paramount with face 
equipment such as the MBC. Even though 
the MBC has several potential advantages, 
most mines would not risk the instal- 
lation and operation of unproven face 
equipment, since any failure would result 
in higher operating costs and lost pro- 
duction. Therefore, the raining industry 
tends to resist the introduction of novel 
raining systems if the in-mine trial does 
not meet anticipated short-term results. 
Even though the most rigorous surface 



test and evaluation program will not sub- 
ject equipment to all of the harsh condi- 
tions found in underground mines, a sur- 
face test program does significantly 
increase the probability that the initial 
underground trial will be successful. 



Surface testing of the MBC commenced in 
September 1982 and final modifications to 
prepare the MBC for in-mine use were com- 
pleted in August 1985. 



DESCRIPTION OF MONORAIL BRIDGE CONVEYOR SYSTEM 



The MBC consists of a series of cascad- 
ing belt conveyors suspended from special 
roof-supported monorail. The MBC-systera 
specifications are shown in table 1. 

The three types of MBC units (inby, 
intermediate, and outby) are shown in 
figure 1. Each unit consists of a belt 
conveyor mounted on a rigid frame, mono- 
rail-suspension hardware, a monorail- 
mounted tram unit, and electric power and 
control components. All MBC units are 
totally monorail suspended except for the 
inby and outby units. The inby end of 
the inby unit is mounted on rubber tires, 
which are steered remotely. The outby 
end of the outby unit can be supported 



either by a dolly mounted on a rigid-belt 
structure or by monorail directly over 
the section belt. See table 1 for de- 
scriptions of various MBC components (in- 
cluding modifications made during the 
test program). 

CONVEYOR UNITS 

Individual conveyor units are fabri- 
cated from hollow structural tubing, pro- 
viding a lightweight and rigid frame. 
Conveyor units are 27 ft, 7 in long over- 
all, with an active length of 24 ft. 
Presently, 12 conveyor units are avail- 
able for a system length of 288 ft; 



wm/m/Mmmm/mmm//mMW//mf//m/m///im//m 




j ggjrts^fe-— ^&^^^4&^ m^ 




Inby unit 



- — --■ T T --" 




Intermediate unit 






Outby unit 



FIGURE 1.— Three types of monorail bridge conveyor units. 



TABLE 1. - Monorail bridge conveyor specifications 

(Prototype system: 12 conveyor units available for 288-ft length; 
expandable to greater length) 



.1.2 



System specifications 

Haulage rate, nominal st/h.. 600 

Tram speed, constant ft/min. . 60 

Electric power requirements, V ac: 

Main system 460 

Control system 120 

Power output, total (for 12 units), hp: 

Conveying 120 

Tramming 20 

Entry width, recommended minimum f t. . 14 

Load, typical maximum on a suspension point lb.. 2,000 

Working height, minimum, in: 

Without low-belt structure 48 

With low-belt structure 54 

Gradability, recommended maximum pet.. 6.5 

Curved-track radius f t. . 24 

Crosscut geometry 3 °. . 60-90 

Individual bridge specifications: 
Dimensions, ft: 
Length: 

Overall 27.6 

Active 24 

Width, overall 

Carrier idlers (on 25° angle), diameter in.. 4 

Rollers, head and tail, diameter in. . 

Belt width in. . 36 

Belt speed, constant ft/min. . 400 

Power output, hp: 

Tram drive motor 1.5 

Conveyor motor 10 

Weight (empty) lb. . 4, 200 



Monorail track: 24-ft radius, designed for 60° crosscuts; available in 7- and 10- 
ft lengths; weight, 7 lb/ft; suspended on 4-ft centers. 
Inby support: remotely steered rubber tires. 

3 90° crosscut: Compound curve must be used with the stipulation that intersecting 
arc lengths must not exceed 30° to prevent interference. 

NOTE. — All units can be controlled by single operator; helper optional. Safety 
features: Belt slip and sequence switches, disk brakes on each tram unit that engage 
automatically when tram power is shut off, emergency stop on each unit, pendant con- 
trol from any unit, end-of-monorail stop on inby unit, and warning horn before belt 
startup. 



however, with electrical modification, 
additional units can be added to provide 
increased system length. A plan view of 
a typical intermediate unit is shown in 
figure 2. A 36-in-wide, 5/16-in-thick 
belt is supported on a conveyor unit with 
a maximum width of 7 ft. Catenary-type, 
4-in-diam carrier idlers are installed 
on a 25° troughing angle. A 1,750-r/min, 
10-hp electric motor powers the belt on 
each unit. A 7:1 double-reduction gear- 
speed reducer is coupled to the head- 
drive roller to provide a constant 400- 
ft/min belt speed, and 7-in-diam crowned 
drive and idler rollers are used. The 
tail idler roller is mounted on an ad- 
justable screw-type takeup. The belt has 
a rated capacity of 600 st/h. Compres- 
sion-spring belt cleaners are mounted 
under the head roller of each unit. 

POWER AND CONTROL 

The MBC is operated by 460-V ac, three- 
phase, 60-Hz electric power provided by a 
No. 2/0 trailing cable to the outby main 
breaker box. Transformers located in 



each motor control box supply 120-V ac, 
single-phase, 60-Hz power for the control 
system. The 10-hp, 440-V ac, single- 
speed conveyor motors and the 1-1/2-hp, 
440-V ac, single-speed, reversing tram 
motors have across-the-line starting. 
The motor control box on each unit is 
equipped with an emergency-stop pushbut- 
ton station that disengages the main cir- 
cuit breaker. 

The electrical system is modular in de- 
sign with identical power and control 
wiring on all but the inby and outby 
units. Figure 3 shows a typical interme- 
diate unit containing the motor control 
case and interconnecting cables common 
to all units. The inby unit has an addi- 
tional control case (fig. 4) that is 
required for the steering motor and head- 
light controls. The outby unit is con- 
nected to two additional control cases 
(fig. 5): the main breaker case, which 
houses the main-system circuit breaker, 
and the master control case, which con- 
tains the emergency-stop controls for the 
entire system. 



Tail roller 



Belt sequence switch 

switch Motor control case 

J i Head roller 




Belt takeup mechanism Troughing idler 



\ 



Coupler 



IO-hp electric motor 



Gear-speed reducer 



•*- Inby 



Note: Belting not shown 

Outby 



FIGURE 2.— Plan view of monorail bridge conveyor unit. 










FIGURE 3.— Intermediate unit. 




FIGURE 4.— Inby unit. 




FIGURE 5.— Outby control boxes. 




FIGURE 6.— Pendant control. 



The MBC system employs automatic se- 
quential belt startup. When the conveyor 
is first activated, an audible warning 
signal is heard. After a brief period 
che signal stops, and the conveyors start 
in sequence beginning with the outby 
unit. Sequence switches allow each suc- 
cessive unit to start only after the pre- 
ceding unit is running at full speed. 
Should a conveyor stop for any reason, 
all conveyors inby the defective unit 
will stop automatically. Each unit has a 
manual ovverride that will operate the 
conveyor on that unit. This control is 
intended for maintenance and diagnostic 
use only. 

Controls for steering, tramming, and 
conveying are located on an umbilical 
pendant control. The pendant control 
(fig. 6) may be connected to any unit in 
the system. This provides operator con- 
venience and allows positioning to avoid 
blind or unsafe MBC operation locations. 
During face operations, the pendant con- 
trol will typically be located on the 
inby unit, so the operator can best con- 
trol the inby steering. 

The MBC system can be trammed on the 
monorail track in both the inby and outby 
directions, with each tram motor equipped 
with an electric brake. The brake re- 
mains set when the machine is stationary. 
Upon activation of the tram control, the 
brake releases and sets again when the 
tram control is deactivated. If a brake 
becomes overheated, it can be manually 
released to prevent further heat buildup. 

Should any unit develop a major mal- 
function requiring it to be removed from 
the system, all electrical connections 
can be disconnected at the plugs and re- 
ceptacles that interconnect the units. 
The units are reconnected in the same 
manner. 

TRAMMING AND SUPPORT SYSTEM 

Both ends of each conveyor unit are 
supported by eight-wheeL carrier assem- 
blies that distribute the weight of 
each conveyor on the monorail track. 
The carriers are designed to follow both 
vertical and horizontal curves in mono- 
rail track without affecting conveyor 
suspension. A 1,100-r/min, 440-V ac, 



1.5-hp traction motor is used for 
tramming each conveyor unit. The motor 
drives two rubber wheels that are held 
against the underside of the monorail 
track. A 24:1 triple-reduction speed re- 
ducer is used to provide a constant tram- 
ming speed of 60 ft/min. Disk brakes on 
each tram motor automatically engage when 
the system is not being trammed. 

Lightweight monorail track is used to 
suspend the MBC system. The inverted 
T-section track, made by Cleveland Tram- 
rail (Cleveland Crane and Engineering, 
Div. of McNeil Corp., Wickliffe, OH) 4 
weighs 7 lb/ft and comes in eight fac- 
tory-available configurations, as illus- 
trated in figure 7. Straight rail is 
available in 14-, 10-, and 7-ft lengths. 
Curved and combination rails in vari- 
ous lengths make 60° turnouts with a 24- 
ft radius. Other lengths and config- 
urations of monorail can be fabricated 
underground to suit particular mine con- 
ditions. A hydraulic rail bender is com- 
mercially available for field-fitting 
curves. Four bolts are used to join 

^Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 



14' 




, u 



LH switch 



10' 

I 



r 

7' 

L 




MK-I MK-2 NIK-6 MK-3 MK-5 MK-4 

straight straight straight curved curved curved 

Note: All curves on 
24-ft radius 

FIGURE 7.— Monorail T-section track configurations with 
designated identification numbers. 



monorail track at overlapping splice 
plates. Both right- and left-hand man- 
ually operated monorail switches are 
available. Figure 8 shows two types of 
hardware that can be used to suspend 
monorail track. One type of suspension 
hardware uses a semirigid connection to 
suspend monorail track from roof plates 
attached to the mine roof with two roof 
bolts. Bevel-headed bolts seated in the 
roof plates are connected to the monorail 
track, allowing limited horizontal track 
movement. A second type of suspension 
hardware enables a nonrigid connection to 
suspend the monorail track using a chain- 
hanger bracket attached to the mine roof 
with one roof bolt. Varying lengths of 
chain connect the monorail track to the 
chain-hanger bracket, allowing horizontal 
and vertical movement of the monorail 
track. 

INBY SUPPORT 

The inby end of the MBC system is sup- 
ported by two 9-in-wide rubber tires 



installed on 38-in centers. The wheels 
are powered by a 1.5-hp electric motor 
at 60-ft/min constant tram speed. The 
tram motor and gear-speed reducer are 
mounted behind the rubber wheels. A sep- 
arate 440-V ac, 1.5-hp electric motor and 
ball thread are used to steer the inby 
wheel carriage. The steering motor is 
controlled from the pendant control. 

The height of the inby conveyor unit 
over the rubber tires is 32 in. The 
height was increased to 40 in with the 
addition of a low-profile hopper. 

OUTBY SUPPORT 

In low-coal applications, the monorail 
track can be offset from the panel belt, 
and the outby end of the MBC can be sup- 
ported by a dolly mounted on rigid belt 
structure (fig. 9) or on a chain panline. 
The dolly ensures transfer onto the panel 
belt without spillage. In higher coal, 
the outby end of the MBC could be sus- 
pended from monorail installed directly 
over the panel belt. 



Chain-hanger assembly 



Roof plat© 




FIGURE 8.— Monorail hardware. 



10 




FIGURE 9.— Outby support with dolly. 



SURFACE TESTING 



Surface tests were conducted to verify 
and measure MBC haulage capability, ma- 
neuverability, power consumption, and re- 
liability. Both rigid- and chain-sus- 
pended monorail track installations were 
evaluated. Numerous modifications were 
made to several MBC subsystems to correct 
deficiencies noted during surface test- 
ing. Important test sequences were re- 
corded on videotape and are available at 
the Pittsburgh Research Center. 

TEST RIG INSTALLATION 

A steel structure was constructed at 
the test facility to support the MBC dur- 
ing surface testing. This test rig (fig. 
10) functioned as a false mine roof and 
was required to suspend the monorail 
track. The test rig enabled MBC testing 
on straight and radius tracks, through 
switches, and on a 6-1/2-pct grade. It 
consisted of nine arches that supported 
underhung beams. Two separate 140-ft 
lengths of monorail track were supported 



from the underhung beams. The two mono- 
rail track sections were parallel to each 
other and offset by 8 ft. Two 80-ft por- 
tions of both monorail tracks were in- 
stalled on a 6-1/2-pct slope. A single, 
60-ft arc length of the 24-ft-radius 
monorail track was connected to the main 
track by a switch. This basic test rig 
was used to support both rigidly bolted 
and chain-suspended monorail tracks. For 
initial test sequences, the monorail 
track was bolted to roof plates that were 
rigidly bolted to the underhung beams. 

A 140 ft length of auxiliary belt 
structure was installed under one of the 
monorail tracks. The belt structure sup- 
ported a 48-in-wide conventional belt 
that operated at 625 ft/min and was pow- 
ered by a 50-hp electric motor. This 
auxiliary belt was used during closed- 
loop coal conveying tests. A beltscale 
weigh bridge was installed in this auxil- 
iary belt to measure the MBC haulage 
rate. 



11 



Offset track t _ 
Main track <L "* 



PLAN VIEW 




Belt-scale weigh bridge 

48 -in auxiliary belt 

£3— 



Switch ^ s 

Radius track 



6 72-pct grade 



Level 



SIDE VIEW 

FIGURE 10.— Surface test rig. 



48- in auxiliary belt 




FIGURE 11.— Monorail bridge conveyor system in test rig. 



Although the MBC consists of 12 con- 
veyor units, only the three (3) unique 
units (inby, intermediate, and outby) 
were used for surface testing because all 
potential MBC configurations could be 
represented using these three units. 

The MBC was installed into the test 
rig using a chain hoist, forklift, and 
mobile crane. First, the eight-wheel 
carrier components were lifted by hand 
and threaded onto an open end of monorail 
track. Next, the tram units and suspen- 
sion frames were moved into position, 
aided by a 1-1/2-st chain hoist. Con- 
veyor units were then moved under the 
suspension frames by forklift and picked 
up by the mobile crane and pinned to the 
suspension frame. Figure 11 shows the 
MBC units installed in the test rig. For 
initial test sequences, the outby end 
of the outby carrier was installed on 
the offset monorail track over the auxil- 
iary belt, and the remaining carriers 
were installed on the main track. No 



difficulties were encountered during in- 
stallation of the MBC units into the 
test rig. Although equipment that would 
not be available underground was used, a 
roof-mounted chain hoist and a scoop car 
could perform the same functions as the 
crane and forklift. After the conveyors 
were suspended, power and control cables 
were installed, and proper tram and 
conveyor-motor electrical operation was 
verified. Tram drive wheels were then 
adjusted to proper tension against the 
bottom of the monorail track, conveyor 
belts were adjusted to track in the cen- 
ter of the idlers, and test personnel 
were trained in proper operation. 

INITIAL CHECKOUT 

After proper MBC operation was veri- 
fied, preliminary tramming and conveyor 
function tests were performed. The MBC 
was trammed through the test rig and into 
the switch several times. The system was 



12 



able to tram upgrade, downgrade, and 
through the switch without difficulty. 
Several modifications were necessary be- 
fore coal handling was possible. The 
power and control cables were shortened 
to proper lengths, because excess weight 
had caused the units to lean toward the 
cables. Spillage guards were added on 
all dump points. (Appendix A lists all 
modifications made during the test pro- 
gram. ) After the modifications were com- 
pleted, preliminary loading trials were 
conducted with all MBC units in straight 
alignment. The MBC was intermittently 
loaded into the inby MBC hopper by a slow 
discharge of coal from the 500-lb capac- 
ity bucket of a skid loader. It was then 
loaded for several minutes by an 8-st- 
capacity shuttle car dumping into the 
inby MBC hopper. No major operational 
problems were encountered with the MBC 
during these tests, and it was able to 
convey coal at normal haulage rates. 

During the initial checkout, a deci- 
sion was made to install an automatic 
steering control for the inby rubber 
wheels. The original manual steering 
wheel, located beside the inby hopper, 
was awkward to operate and potentially 
unsafe. New gearing, a mounting bracket, 
an electric motor, and a control switch 
were installed. 

POWER CONSUMPTION 

Power-consumption trials were conducted 
to determine overall system electrical 
characteristics and to specifically in- 
vestigate if the number of tram motors 
could be decreased without affecting 
system performance. Each MBC unit is 
equipped with one monorail tram drive. 
An additional rubber-wheel tram drive is 
used on the inby unit. The rubber- 
wheeled tram drive on the inby unit, lo- 
cated several inches off the ground, was 
determined to be in an undesirable loca- 
tion because of potential water damage 
and ground clearance problems. There- 
fore, it was desirable to eliminate this 
motor, but only if doing so would not 
overload the remaining motors. For the 
power-consumption trials, the number and 
location of the tram motors were varied 
for both loaded and unloaded conveyors, 



and for upgrade and downgrade gradients. 
The test variables and results of these 
trials are listed in table 2. 

The power consumption of the MBC tram 
motors was monitored by utilizing a cur- 
rent transformer with a ratio of 150:5 on 
the A and C phase legs of the MBC power 
cable. The current transformers were 
connected to transducers, which provided 
a 0- to 10-V dc output for a 0- to 120-kW 
power span. The current transformers had 
a factory-stated accuracy of ±1 pet. The 
watt transducers had a stated accuracy of 
±0.25 pet. All power-consumption data 
were recorded by an eight-channel strip- 
chart recorder. Channel calibration was 
performed before each test. 

For each test, the power-consumption 
instrumentation and recorder were acti- 
vated, and the MBC system was trammed 
through predetermined start and stop 
points. The floor area underneath the 
inby unit was cleaned so that the rolling 
resistance of the inby rubber wheel would 
not vary. 

For all trials (table 2) except G, H, 
I, and J, the original roller chain drive 
on the inby rubber wheels was connected. 
(This original roller chain drive was 
later replaced with a sealed, gear-speed- 
reducer driver. ) For the trials using 
three rail motors (E, F, G, H, I, and J), 
the rubber-wheeled tram drive was elec- 
trically disconnected. For the trials 
using only two rail motors (S, T, V, W), 
only the monorail tram drives on the inby 
and outby units were operated, and the 
inby rubber-wheeled tram drive and inter- 
mediate unit monorail tram drive were 
electrically disconnected. For the tri- 
als using four rail motors (X, Y, Z, and 
AA), an additional tram motor was in- 
stalled on the monorail immediately outby 
the inby unit tram motor. These two tram 
motors were connected by a short drawbar. 

For trials A through (table 2), the 
average power consumption for both level 
and 6-1/2-pct-grade track was determined. 
The power consumption for a 20-ft length 
of track, at the start of upgrade trials 
and at the end of downgrade trials (fig. 
11), was used for the level, kW on level 
track column of table 2. The power 
consumption for a 10-ft length of track, 
at the end of the upgrade trials and at 



13 



TABLE 2. 


- Monorail 


bridge 


convey 


or power 


consumpt ion 




Trial 




Motors used 


Level, 1 

av kW 


Grade, 
av kW 


Peak, 

kW 


Design, 




Rail 


Wheel 


max kW 







UPGRADE 


GRADIENT 








Conveyors 
A 


unloaded: 




3 

3 

2 3 

2 

4 

3 

2 3 

3 

4 


1 





1 





2.8 
2.0 
1.8 
( 3 ) 
( 3 ) 

2.9 
2.0 
( 3 ) 
( 3 ) 


4.1 
3.5 
3.4 
3.4 
4.3 

4.7 
4.0 
4.0 
4.7 


5.0 
3.8 
3.6 
3.6 

4.8 

5.8 
4.8 
4.2 
5.8 


4.5 


E 


3.4 


G 


3.4 


s 


2.2 


z r 


4.5 


Conveyors 



loaded: 




4.5 


J 


3.4 


W 


2.2 




4.5 







DOWNGRADE 


GRADIENT 








Conveyors 
B 


unloaded: 




3 
3 
2 3 
2 
4 

2 3 
3 
2 
4 


1 
1 






1 





2.8 

1.9 
1.7 
( 3 ) 
( 2 ) 

2.0 
2.9 
( 3 ) 
( 3 ) 


1.4 
.7 
.5 
.5 

1.3 

.4 
1.3 

.4 
1.1 


3.4 
2.2 
1.8 
2.3 
2.9 

2.2 
3.1 
3.1 
3.1 


4.5 


F 


3.4 


H 


3.4 


T 


2.2 


AA 


4.5 


Conveyors 
I 


loaded: 




3.4 


N 


4.5 


V. . . 


2.2 




4.5 



For "upgrade gradient," the units were traveling from right to left, and 
for "downgrade gradient," the units were traveling from left to right on the 
level portion of track. 

Rubber-wheeled tram drive electrically and mechanically disconnected for 
these trials. 

Test configurations did not permit power readings on level track sections. 




the beginning of the downgrade trials, 
was used for the "Grade, av kW" (6-1/2- 
pct) column of table 2. Between these 
points, the grade traveled by each tram 
motor varied. 

The strip-chart data were visually 
averaged for both the "level" and "grade" 
kilowatt values. The "Peak, kW" column 
of table 2 was taken as the maximum in- 
stantaneous power draw recorded by the 
strip chart for each trial (exclusive of 
starting power). The "Design, max kW" 
column of table 2 was obtained by multi- 
plying the number of tram motors used and 
the nameplate horsepower rating by the 
conversion factor for horsepower and 
kilowatt. 

For trials S through AA, only the aver- 
age and peak power consumptions for the 
6-1/2-pct grade were determined, because 
the test-rig configuration did not allow 



the MBC system to tram on the entire lev- 
el track section. 

Figure 12 shows the strip-chart read- 
outs from two typical trials. For trial 
J, three rail motors were used on the 
loaded MBC system, and the average power 
consumption while tramming up the grade 
was 18 pet over the design maximum power 
draw. For trial 0, three rail motors and 
the inby rubber-wheel tram drive were 
connected, and the average power consump- 
tion while tramming upgrade was 4 pet 
over the design maximum power draw. For 
both trials, power consumption while 
tramming on the level was below the de- 
sign maximum. These data indicate that 
the inby rubber-wheel tram drive would be 
removed if the system normally operates 
on a level grade; however, tram-motor 
life would be shortened if the system 
must regularly tram upgrade. 



14 



DISABLED BRAKE TEST 

The objective of the disabled brake 
test was to determine if the loaded MBC 
system would safely hold while station- 
ary on the 6-1/2-pct grade with a dis- 
abled brake. The loaded MBC system was 
trammed into the 6-1/2-pct grade rack 
section, and the brake on the inby unit 
was electrically deactivated. The sys- 
tem remained stationary. Next, the inby 
and intermediate unit brakes were 



4 — 



« i I I I I I I I I I I I I I I | I I I I I I | I I I I 
Trial J 
Loaded, upgrade 3rail motors 

[Grade 



• Level 



-3.4-kWdesign,maximum 



2 



s |2 r 



-Level 



1 ' ' ' ' ' ' ' I ' ' 'tridlO » ' l i i I i i I. 
Loaded upgrade 3 rail motor, I wheel motor ; 

^ /4.5-kW design, maximum 



~vAv v * 



10 



I I I I I 



■ I ■ 



20 



25 



FIGURE 12.— Typical power-consumption plots. 



deactivated, and the system remained 
stationary while being held only by the 
outby brake. The disabled brake test 
verified that the system can be safely 
operated on a grade, even if several 
brakes are temporarily disconnected. 

HAULAGE RATE 

The objective of the haulage-rate tests 
was to determine the maximum haulage ca- 
pacity of the MBC units and to investi- 
gate spillage sources. To measure the 
instantaneous and total weights of coal 
moved by the MBC system, an electronic 
belt-scale system installed on the 48-in- 
wide auxiliary belt was used. To obtain 
a high haulage rate, the MBC system was 
installed in a closed-loop configuration 
(fig. 13). The MBC system was located in 
the radius portion of the test rig. The 
outby MBC unit dumped coal onto the 
auxiliary belt, which dumped onto a 30- 
ft-long, 36-in-wide flat belt. The flat 
belt then dumped coal into a shuttle car, 
which dumped back into the inby MBC unit 
hopper. Run-of-mine (ROM) bituminous 




Conventional belt units 



Shuttle car 



FIGURE 13.— Closed-loop configuration. 



15 



coal was added to the system by loading 
coal into the shuttle car. 

The MBC was located in the radius por- 
tion of the test rig so that the inby and 
intermediate MBC units were at a 43° an- 
gle to each other. This worst-case con- 
figuration (fig. 14) occurred where the 
two conveyors intersected at the cen- 
ter of the 60° arc of the radius track 
section. 

During initial trials, belt-alignment 
problems were encountered on the inter- 
mediate unit. Prior to loading, the 
belts were adjusted at the takeup to 
track in the center of the rollers, but 
the belts untracked as soon as the belts 
were loaded. Be It -alignment problems 
were not encountered during the initial 
checkout haulage test when the MBC units 
were in straight alignment. It is as- 
sumed that the alignment problems were 
caused by side loading from the inby 
unit. With the inby and intermediate 
units installed at an angle, coal at 
the transfer point from the discharging 
conveyor had momentum perpendicular to 
the axis of the receiving conveyor. The 



belt would misalign in response to this 
side loading. Problems with coal dis- 
charging from the inby unit and hitting 
the suspension frame of the intermediate 
belt also contributed to the belt-align- 
ment problem, since spillage was falling 
onto the return side of the intermediate 
unit belt and jamming the tail roller. 
Because of these belt-alignment problems, 
two modifications were made before fur- 
ther trials were attempted: (1) a 3/16- 
in/ft crown taper was put onto the head 
and tail rollers, and (2) the suspension 
frame was modified to provide more area 
for the coal to discharge. Crown taper 
is commonly used on belt conveyor rollers 
to improve tracking. Conveyor belts tend 
to move toward the direction of great- 
est tension, and the crown taper causes 
the conveyor-belt tension to be greatest 
at the center of the head and drive 
rollers, thus making the conveyor belt 
self-centered. 

After the above modifications were com- 
pleted, the haulage-rate trials were re- 
started. Figure 15 shows the strip-chart 
readout for the haulage-rate trial. An 




FIGURE 14.— Monorail bridge conveyor units at maximum-angle relationship. 



16 



1,200 




10 
TIME, s 

FIGURE 15.— Haulage-rate plot. 



8§ '> 200 

2 K -C 

< O ^ 800 
I- 2 «/> 



p 3 



"i — i — i — | — i — i — i — t 
Adding coai- 



t — i — r— i — i — r 



-i—\ — r 



TZ 



j^/amJHV *^ |l^f^7^ > *^^*^^**H*Mw4*<'^M>i*y w * l ^i 



400 

0t i i i i I i_i 



J I l_l I l_l I I L 



J I I I l__L 




20 



-i — i — i — r 



J ■ ■ ■ i, 



25 



15 
TIME, s 

FIGURE 16.— Haulage rate and power plots during maximum haulage-rate trial. 



30 



average of 450 st/h of coal was handled 
without experiencing problems with the 
MBC system. The decreasing haulage rate, 
after coal addition was stopped, was due 
to spillage at the shuttle car. Spill- 
age at the MBC transfer points was 
negligible. 

A second test was conducted to estab- 
lish the maximum haulage rate of the MBC 
system. Belt-motor power consumption was 
monitored during this test, in addition 
to haulage rate. Coal was added to the 
closed-loop circuit until failure of the 
flat auxiliary belt precluded additional 
loading. The peak instantaneous loading 
rate during this trial was 600 st/h (fig. 
16). No problems were observed with 
the MBC system during peak loading rates. 
All belts remained in alignment, and 
spillage at the transfer points was mini- 
mal. The maximum observed conveyor-motor 
power consumption was 16.8 kW for three 



motors. These tests verified that the 
MBC is capable of haulage at its design 
specification of 600 st/h. 

MINER LOADING TRIALS 

The objective of the miner loading tri- 
als was to verify the ability of the MBC 
to simultaneously tram and receive coal 
from the discharge boom of a continuous 
miner, as would be done underground. A 
Joy 16CM continuous miner was used to 
load directly into the hopper of the inby 
unit (fig. 17). The miner had a 24-in- 
wide and 8-in-deep chain conveyor area. 
A 15-st pile of wetted ROM bituminous 
coal was placed in front of the contin- 
uous miner. The continuous miner was 
positioned inby the MBC system, which 
was located in the radius portion of the 
test rig. The outby MBC unit discharged 
onto the 48-in auxiliary belt. A 10-st 



17 




FIGURE 17.— Continuous miner loading directly into monorail bridge conveyor. 



capacity shuttle car was used to receive 
coal discharged from the auxiliary belt. 
For each trial, the instantaneous load- 
ing-rate instrumentation was started, the 
miner was trammed into the coal pile, and 
the miner operator directed the miner 
tail boom toward the MBC hopper. The MBC 
operator, located beside the inby MBC 
motor-control case, trammed and steered 
the MBC system as required to locate the 
MBC hopper under the discharge from the 
continuous miner. The miner advanced ap- 
proximately 15 ft into the coal pile un- 
til the pile was eliminated. After each 
trial, the MBC and miner were backed up, 
and the shuttle car dumped the coal in 
front of the continuous miner. For sev- 
eral trials, the miner was maneuvered to 
simulate coal face cleanup operations. 
Total tonnage for each trial was deter- 
mined from the belt-scale totalizer. The 
total tonnage loaded and maximum instan- 
taneous MBC haulage rate for each trial 
were: 

Trial A - 10.1 st loaded at a maximum 
rate of 690 st/h. 



Trial B - 8.2 st loaded at a maximum 
rate of 720 st/h. 

Trial C - 12.9 st at a maximum rate of 
720 st/h. 

Trial D - 10.0 st loaded at a maximum 
rate of 630 st/h. 

Trial E - 7.6 st loaded at a maximum 
rate of 660 st/h. 

The miner operator had no problems 
keeping the inby hopper of the MBC under 
the miner tail boom as the miner trammed 
into the coal pile. The MBC operator was 
also able to maneuver behind the mine 
during face cleanup operations. This 
test sequence verified the ability of the 
MBC to simultaneously convey coal and 
tram. 

RELIABILITY 

To determine the reliability of the 
conveyor portion of the MBC system, 
the MBC was installed in a stationary 



18 



closed-loop configuration. ROM bitumi- 
nous coal was added to the circuit by 
slow discharges from a 500-lb capacity 
loader bucket into the hopper of the inby 
unit. Coal continued to be added until 
the belt-scale output showed an average 
rate of 500 st/h. Recharges of coal were 
occasionally necessary when spillage 
losses in the circuit caused the rate to 
fall to 300 st/h. All coal was wetted 
prior to loading for dust control. 

For the entire trial, the instantaneous 
loading rate, the 48-in auxiliary belt 
speed, the belt-scale load-cell output, 
and the total MBC power consumption were 
plotted on a strip-chart recorder. Dur- 
ing the reliability trial, an event log 
was maintained. Event description, time, 
MBC conveyor hourmeter and totalizer 
readings were recorded for each test 
event. Water was applied to the under- 
side of each MBC belt every hour to con- 
trol dust generation. 

During the reliability trial, the MBC 
conveyors loaded 2,141 st of ROM coal 



during 5.7 h, for an average loading rate 
of 375 st/h. Loading-rate peaks of 600 
st/h occurred several times during the 
trial. One failure occurred at 1.3 h 
into the trial: The conveyor drive cou- 
pler on the inby MBC unit came apart 
while the system was hauling at 400 st/h. 
To repair the coupler, the conveyor drive 
assembly was realigned with respect to 
the head drive shaft, and the coupler was 
replaced. The repair was accomplished by 
two mechanics in approximately 2 h. One 
adjustment was necessary at 4.1 h into 
the trial because it was observed that 
the outby unit belt was misaligned by 
several inches. The belt takeup was 
quickly adjusted without interfering with 
coal haulage. 

Figure 18 shows two 36-min, instantane- 
ous loading rate, and total MBC power- 
consumption traces. The upper trace oc- 
curred at 3. 1 h into the trial. After 
coal addition stopped, the average load- 
ing rate was approximately 390 st/h. The 
average power consumption for the same 



V) 



111 



5 t- 1,200 |- 
w a: 900 





600 
300 


V) 
Z -J 


O 


■£ 

or 


24 
20 



-1 — r — 1 — 1 — 1 — 1 — 1 — r — 1 — 1 — 1 — 1 — 1 — r— 1 — 1 — 1 — r — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — p — 1 — 1 — 1 — 1 — r 

»■• Adding coal »h 



lL U U « *»44.J' UM t» U * M i 



1 — 1 1 1 1 1 1 i_i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 — 1 1 




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16 - 



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■ 1 'I ' i ' 1 1 ' 1 ' 1 ' 1 ' ■ 1 ■ 



J I I I L J I I I I I 1 I I I I I 1 1 1 I 1 l_ 



TRIAL B TIME 



CHART SPEED= O.lmm/s 

FIGURE 18. — Loading rate and power consumption during reliability trial. 



19 



time was approximately 11 kW or approxi- 
mately 15 hp; i.e., half the rated motor 
capacity of 30 hp. The scattered peaks 
and variations in power consumption were 
probably due to very fast openings and 
closings of one or more of the belt-slip 
centrifugal switches, which in turn shut 
the conveyor belt motors on and off. MBC 
belt-speed variations were not noticed 
during power-consumption variations. 

The bottom trace was acquired at 4.1 h 
into the trial when the system was being 
restarted after a lunch break. After 
coal addition stopped, the average load- 
ing rate was 480 st/h. The average power 
consumption for the same time was 12.5 
kW. Observed variations in both total 
MBC power consumption and loading rate 
were dampened with time because of more 
equal distribution of coal in the cir- 
cuit. Midway through the bottom trace, a 
belt-slip switch was opened while the 
left was being cleaned. The belt clean- 
ers at that time were tensioned against 
the return belt by a counter-weight of a 
lever arm. By pulling the lever arm, ex- 
tra force could be applied to the belt 



cleaner. In this instance, extra force 
applied to the belt cleaner caused the 
return belt to raise and lose contact 
with the slip-switch roller. After these 
trials, the counterweighted belt cleaners 
were replaced with a compression-spring 
tensioner device. 

The reliability trial was terminated at 
5.7 h into the trial because of a spill 
at the intermediate discharge point that 
was caused by excessive coal flow, which 
buckled the hoop-type deflector. Coal 
was being added to the system at the 
time, and the haulage rate exceeded 600 
st/h. This spill contributed greatly to 
the total spillage amount that had accu- 
mulated at the inby discharge point. Af- 
ter the trial, spillage at both the inby 
and intermediate transfer points was 
raised. There was 700 lb of spillage un- 
der the inby transfer point, and 4,650 lb 
of spillage under the intermediate trans- 
fer point. Figure 19 shows the spillage 
under the inby transfer point. Prior to 
the spill, it was observed that spillage 
under the intermediate transfer point was 
twice the amount under the inby transfer 




FIGURE 19.— Spillage under inby monorail bridge conveyor transfer point. 



20 



point, or approximately 1,400 lb. Based 
on the lower prespill assumed value, 
2,100 lb of spillage occurred during the 
trial, and the total amount of coal 
loaded was 2,141 st. Spillage rate dur- 
ing this trial can then be computed as 
0.05 pet of throughput. It is likely 
that the spillage rate might be higher 
during in-mine operation, since the sys- 
tem would be occasionally tramming during 
conveying operations. During the entire 
reliability trial, the inby and interme- 
diate conveyors were at a 5° angle to 
each other, and the intermediate and 
outby conveyors were at 20° angles. Dur- 
ing previous trials, it was observed that 
the amount of spillage at transfer points 
increased rapidly as the angle between 
the conveyor increased. After the tests, 
the center of the hoop-type deflector was 
bolted to the suspension frame to prevent 
future buckling. 

SYSTEM COMPATIBILITY 
WITH LOW-BELT STRUCTURE 

There are several ways that the outby 
end of the MBC can be located to ensure 
smooth coal transfer onto the section 
belt: One way is to suspend the outby 
unit from the monorail installed di- 
rectly over the section belt, and another 
is to attach the outby end of the outby 
unit to a dolly supported by a low-belt 
structure. 

To demonstrate the compatibility of the 
MBC system with a commercially available 
low-belt structure, a 32-ft-long section 
of low-belt structure and a dolly were 
installed under the chain-suspended right 
monorail track (fig. 9). The frame of 
the low-belt structure, designed for use 
with a 42-in-wide belt, was made of in- 
terlocking roller assemblies and connect- 
ing members. The low-belt structure was 
extended to a total length of 32 ft by 
the addition of framework made of 5—1/2— 
in-wide channel sections. Rollers on the 
bottom and cams on the side of the mating 
dolly allowed easy mobility on the frame 
of the low-belt structure. The low-belt 
dolly was modified by adding an attach- 
ment bracket. This bracket firmly at- 
tached the outby MBC unit to the low-belt 
dolly, while permitting the outby unit to 



pivot in both horizontal and vertical 
directions. A 42-in-long drawbar was at- 
tached between the tram outby motor and 
dolly bracket. The main power cable to 
the MBC was then attached to the strain- 
relief clamp of the low-belt dolly, so 
that the power cable would always move 
with the system. 

No problems were observed as the en- 
tire MBC system and dolly were repeatedly 
trammed along the 32-ft, low-belt struc- 
ture in the inby and outby directions. 
The dolly moved smoothly on the low-belt 
structure; the only jerking motion oc- 
curred during starting and stopping be- 
cause the outby tram motor was not rigid- 
ly attached to the outby MBC unit. When 
the system started tramming, force from 
the outby tram motor pushing against the 
drawbar tended to briefly lift the outby 
motor and suspended monorail track. How- 
ever, steady-state tramming motion was 
quickly reached within 2 s because all 
tram motors were operated at the same 
speed. 

The material-handling capability of the 
dolly-mounted MBC system was not tested. 
It is expected that transfer of material 
from the outby MBC unit to the panel belt 
would not be a problem in a dolly-mounted 
configuration, since the dolly fixes the 
outby unit at a constant height from the 
panel belt, and skirt boards can be added 
to the dolly as required. 

SUSPENSION OF MONORAIL TRACK 
BY CHAIN HANGERS 

There are several ways of installing 
special monorail track from the mine 
roof: One is to rigidly attach the track 
to roof plates anchored to the mine roof. 
Another method is to chain-suspend the 
monorail track from chain-hanger brackets 
anchored to the mine roof. Roof plates 
minimize the head room required for sus- 
pension hardware, but they are difficult 
to adjust and require two roof bolts. 
Chain hangers allow easy height adjust- 
ment and require only one roof bolt, 
but require extra head room. Initial 
test sequences were performed with the 
monorail track rigidly attached to roof 
plates. To determine if the MBC system 
could tram on freely suspended monorail 



21 



Chain 




FIGURE 20.— Profile of chain-suspended monorail track. 




FIGURE 21.— Chain hanger. 

rail track, a 50-ft section of the right 
monorail track was suspended from chain 
hangers (fig. 20). To suspend the mono- 
rail track, chain-hanger assemblies, us- 
ing various-length, 1/4-in high-strength 
alloy steel chain with attachment hard- 
ware, were hung from the roof -bolt mount- 
ing plates on 4-ft centers. Each chain 
was held to the simulated mine roof by 
a chain-hanger bracket, which permitted 
adjustable chain height. The chain 
was connected to the top of the monorail 
track by a 1/2-in hex bolt welded to a 
chain clevis (fig. 21). 



A hydraulically powered rail bender 
was utilized to make concave and convex 
vertical curves in the inverted T-section 
monorail track. The rail bender was op- 
erated by clamping a section of monorail 
track between a load ram and two pivot 
points. The load ram was activated by 
means of a hydraulic handpump. By us- 
ing a displacement indicator on the rail 
bender, specific angles could be made in 
the track. The radius of the bend could 
be controlled by changing the distance 
between the load ram and pivot points. 
The rail bender was then used to install 
two convex bends of 3.7°, 32 in apart, on 
the first 7-ft-long monorail track sec- 
tion. This track section, previously on 
a 6-1/2-pct upward grade, was bent to end 
with a 6-1/2-pct downward grade. Addi- 
tional track sections were then connected 
to give the track a straight 6-1/2-pct 
downgrade. When the top of the track 
reached a height of 68 in from the 
ground, a single concave bend was made so 
that the end segment of the track was 
parallel to the ground. In all cases, 
each 7-ft-long track section was sus- 
pended from the support structure by 
chain hangers on 4-ft centers before the 
next track section was connected. After 
the entire 50-ft section of track was 
suspended, several of the chain-hanger 
lengths required adjustment to prevent 
slack in the hanger assembly. The height 
was adjusted by changing the chain link 
in the adjustable hanging bracket. To 
constrain sideways movement, 1/4-in chain 
installed perpendicular to the monorail 
tracks was used at the outby end of the 
suspended monorail track. 

After the 50-ft segment of monorail 
track was suspended, the outby end of the 
outby MBC unit was mounted on a low- 
belt dolly, as described in the previous 



22 



section. The ability of the MBC system 
to tram on chain-suspended monorail track 
was then observed. 

No problems were experienced as the 
dolly-mounted MBC system was repeatedly 
trammed in both the inby and outby di- 
rections on the chain-suspended mono- 
rail track. The eight-wheel carrier as- 
semblies negotiated a 13-pct change in 
grade over a 3-ft distance without any 
noticeable binding. Sideways movement 
of the suspended monorail track was not 
observed. 

SYSTEM COMPATIBILITY WITH HOPPER-FEEDER 

Although the inby MBC unit can be 
loaded directly by a continuous miner, in 
most cases, it would be desirable to In- 
clude surge and breaker capabilities be- 
tween the miner and the MBC. The Bureau 
has developed a separate prototype mining 
machine, the hopper-feeder-bolter (HFB), 
to perform that task. The HFB is a cat- 
mounted vehicle that includes a 5-st ca- 
pacity surge hopper, an onboard lump 
breaker, a variable-angle discharge boom 
and an optional bolter-module (fig. 22) 
to permit bolting beside a two-pass con- 
tinuous miner. This provides the advan- 
tage of eliminating face-to-face place 



changes during the mining cycle. The 
bolter module was removed and only the 
hopper-feeder (HF) was used during trials 
with the MBC. 

To evaluate the ability of the HF to 
load the MBC, a compatibility trial was 
conducted. The HF was located inby the 
MBC, and the MBC was loaded with coal 
discharged from the HF. The low-profile 
hopper on the MBC was removed to enable 
the 16-in profile HF discharge boom to 
fit between the top of the inby MBC unit 
(32 in) and the underside of the monorail 
track (59 in). As shown in figure 23, 
there was little clearance between the HF 
boom and the top of the inby MBC unit and 
a very small target area on the MBC to 
permit loading without spillage. During 
the loading trial, the MBC was able to 
haul all coal being discharged at the 
maximum HF loading rate; however, exces- 
sive spillage was observed at the trans- 
fer point between units. An improved in- 
terface between units would be required 
before they could be used together. 
Since the HF boom must clear the under- 
side of the monorail track, the exact de- 
sign of the interface will depend upon 
the height of the monorail installation 
at the mine site. 



SUMMARY OF SURFACE TEST FINDINGS 



Surface testing verified that the MBC 
system properly performs its design func- 
tions and is worthy of an in-mine trial. 
Hightlights of the surface test program 
are summarized below. 



power consumption was 
several tram-motor 



• Tram-motor 
measured for 
configurations. 

• The braking system is more than ade- 
quate, as one functioning brake unit held 
three loaded MBC units on a 6-1/2-pct 
grade. 

• The ability to haul the design ca- 
pacity of 600 st/h was verified. 

• The MBC was capable of being loaded 
by a continuous miner. A maximum haulage 



rate of 720 st/h was measured during the 
miner loading trials. 

• During a reliability trial, the MBC 
system loaded 2,141 st of coal in 5.7 h 
with only one minor coupler failure. 

• The MBC was trammed with the outby 
end supported by a dolly mounted on a 
low-belt structure. 

• The MBC was able to tram from mono- 
rail suspended from roof plates and chain 
hangers. 

• The MBC is compatible with the HF, 
which provides surge capacity and lump- 
breaking capability inby the MBC. An im- 
proved interface between the MBC and HFB 
is required to suit mine conditions. 



MODIFICATIONS 



Numerous modifications were made to the 
original system design to correct the 
problems observed during surface testing. 



A complete listing of modifications is 
contained in appendix A. Major modifica- 
tions included. 



23 



*sa^ 




FIGURE 22.— Hopper-feeder-bolter. 




FIGURE 23.— Hopper- feeder compatibility trial. 



24 



• Conveyor belt head and tail rollers 
were crowned to improve belt tracking. 

• The clearance area in suspension 
frames was increased to create more area 
for coal transfer between conveyors. 

• Deflectors to direct coal flow and 
control spillage were installed at con- 
veyor transfer points; belt cleaners 
were installed on the underside of each 
conveyor. 

• Remote-controlled steering was 
installed. 

• A limit switch to prevent the system 
from tramming at the end of the monorail 
was installed. 

• A lightweight pendant control was 
installed. 

• The wheel base of the inby wheels 
was increased for greater stability. 

• The control circuitry was changed to 
utilize an intrinsically safe control 
pendant. 

MINING 



The review process for the MSHA experi- 
mental permit was initiated in December 
1984. Review of the control circuitry 
revealed some problems. The system was 
designed with intrinsically safe control 
circuitry intermingled with 120-V ac pow- 
er in a multiconductor control cable. To 
remedy this situation, 480- to 120-V ac 
transformers were installed into each 
motor control box and additional safe 
isolation relays were installed. The 
main contactor allowed 120-V ac power in- 
to each control box even when the main 
switch was in the "off" position; this 
was corrected by replacing the original 
contactor in the master control box with 
a circuit breaker located in a separate 
enclosure. The changes made to meet MSHA 
requirements are listed in appendix A. 



PLANS 



Based upon observations made during 
surface testing, the following mine re- 
quirements are suggested: 

• The minimum working height of the 
MBC is 48 in. The minimum working height 
increases to 54 in if the outby end of 
the MBC is supoprted by a 6-in high low- 
belt structure (figs. 24-25). Additional 
working clearance would ease cleanup un- 
der the MBC. 



• Maximum gradability of the system 
is 6.5 pet without excessive tram motor 
wear. Greater grades can be negotiated 
at the expense of decreased tram-motor 
life. 

• A minimum entry width of 14 ft is 
possible if 60° crosscuts are used and 
intersection corners are rounded; how- 
ever, a wider entry is desirable to allow 
a walkway at all points on the clearance 
(right) side of the system. 



Roof bolt (typical load 2,0001b) 




hanger 



FIGURE 24. — Monorail installation with chain hangers. 



25 



4" reference 



Outbyunit 
control box 




54 M min 




.5-hp 



Monorail track -^ 
■•— | n by tram motor 

Belt direction — Drawbar 




Main power cable 



T 

8" reference 



Power and control cables to other units 



Low-belt structure Belt direction -»► 



(panel belt) 

FIGURE 25.— Monorail installation with roof plates over low-belt structure. 




60° SIMPLE CURVE 
System con be used ; _ 

29° angle between A~B and BC 
is <40° 

NOTES: 

Maximum angle between units is 40°, 
Only RH turnouts are shown. 
Angle of switches, 11°. 
Arc of track sections: MK-3 and 
MK-5, 12°; MK-4, 24°; MK-7, 19°; 
andMK-8,3l°. (MK-7andMK-8 
track not available at time of tests.) 
All track curves on 24- ft radiurs. 
All track is shown centered in 18-ft 
entry. 



_1 



*^o Crib or post -»Q 




*G 



90° SIMPLE CURVE 
System cannot be used; 
49° angle between AB and 
BC is > 40° 




90° COMPOUND CURVE 

System can be used; 

34° angle between BC and C~D 

is <40°. 

However, 2 x FH=2 x 39ft=78ft. 

This is too wide. Mine would require 

extra roof support so that 2 x GH 

<70ft. 



KEY 

■ Splice plate 
MK-5 Track designation 
AB Represent units (each 24-ft long) 
PT Point of tangency 



FIGURE 26.— Monorail bridge conveyor track turnout plans. 



26 



• The MBC was designed for 60° cross- 
cuts using the 24-ft radius monorail 
track, however, crosscuts of 90° can be 
negotiated using a compound curve. In 
any turnout configuration, the angle be- 
tween MBC units must be less than 34° to 
prevent unit-frame interference with each 
other. An advantage of 60° crosscuts 
is that spillage between units will be 
minimized because potential spillage at 
transfer points increases as the angle 
between units increases. Figure 26 shows 
track installation plans for both 60° and 
90° crosscuts. 

• Suporting the MBC system should not 
be a problem because the eight-wheel car- 
riers distribute conveyor weight over a 
6-ft length of monorail track, which re- 
sults in a typical load on each suspen- 
sion point of less than 1 st. Although 
not tested, resin bolts are recommended 
over mechanical bolts to better withstand 
tramming-induced vibration. 



The MBC can be used for room-and-pillar 
mining (figs. 27-29), longwall develop- 
ment (fig. 30), or shortwall mining (fig. 
31). For room-and-pillar mine plans, the 
monorail track does not have to be in- 
stalled in all mine entries. As illus- 
trated in figure 27, the monorail track 
would typically be installed over or 
beside the panel belt in the center en- 
try and in each crosscut. The combined 
length of the inby MBC unit and the con- 
tinuous miner enables raining in entries 
that do not have monorail track in- 
stalled. The hopper of the inby MBC unit 
can be up to 20 ft from the last point 
of monorail suspension. Assuming that a 
typical continuous miner is 35 ft long, 
the continuous miner cutterhead can be 
up to 55 ft from the last point of mono- 
rail installation (fig. 32). Various cut 
plans are possible, depending on local 
conditions. 



Continuous miner 



HFB surge car 




1 2-unit system 



Monorail track 



FIGURE 27.— Five-entry mine plan. 



27 




FIGURE 28.— Five-entry 60° mine plan with rooms. 



M 



5 | 12 10 



23 



26 24 22 



20 



16 

1a 



27 29 31 



^>K 



■ I 



LEGEND 
[7] Cut number 



32 35 37 



40 



E*lE 



M 



1 l 1 1 1 > 1 » 1 * 1 1 H * l 1 



v !y 1 . 1 1 . 



39 41 M3 45 



J--75- 



•J 



< t I » 1 1 ' 1 1 in 1 1 1 1 1 1 1 1 1 n 1 1 ^ ■ 



«^ ^| l| >immm 1 > ■ t > 1 « » » i 



I I M I I I > » » I t ■ < t * ) I » I I » 




■ I I I I M l I MM Ml IM I i l M 



-18' 



Return Intake Intake Be 

FIGURE 29.— Seven-entry mine plan 



t Track Intake Return 
(power) 



28 



Panel belt 



MBC system Monorail track 



Belt 



Intake 



Return 




60° (typical) 



FIGURE 30.— Mine plan for longwall panel-entry development. 



mm mm 



-r-Panel belt conveyor 



:}:<~rj:!: 







MBC system 

Continuous miner 




mm ml 



Jr.- "I ^_J : ' 



,■„ ' . ' : ' ? . 9 l t . ' ■■..■ - ■-. ! 



„ Chock 

FIGURE 31.— Monorail bridge conveyor used with shortwall mining system. 



■fSKAtt* 



A potential application of the MBC sys- 
tem would be in longwall panel develop- 
ment. As shown in figure 30, the 288-ft 
MBC system would be of sufficient length 
to advance two crosscuts of a three-entry 
heading, thereby potentially reducing 
longwall-panel development time. 

An alternate use of the MBC system 
would be to provide continuous haulage 
capability for shortwall raining sec- 
tions. Shortwall raining has the poten- 
tial to provide productivity advantages 



of longwall raining without high capital 
costs. A major impediment to more short- 
wall application is the lack of a contin- 
uous haulage system. As shown in figure 
31, the MBC connects the continuous miner 
to the panel-belt conveyor with the mono- 
rail track bolted to mine roof in the 
headgate entry. In the face area, the 
monorail is supported underneath chocks 
with the provision that the lightweight 
monorail track could be manually con- 
nected after the chocks are advanced. 



29 




rf5L.-L -„ 

7 I^=m^m//=//7rm/r//i^/////L 



55' 



FIGURE 32.— Monorail bridge conveyor with continuous miner. 




FIGURE 33.— Hopper-feeder-bolter. 



If oversize material (over 12 in) is 
regularly encountered during the mining 
cycle, a crusher should be used inby the 
MBC system to avoid clogging MBC trans- 
fer points. The previously described 
HFB with optional bolter removed, shown 
in figure 33, can perform that task. 
Additional advantages of using the HFB 
between the continuous miner and MBC 



are that (1) surge capacity is provided; 
(2) an outby feeder breaker can be elimi- 
nated; and (3) extra system reach is pro- 
vided. As seen in figure 34, the contin- 
uous miner cutterhead can be up to 80 ft 
from the last point of monorail installa- 
tion. If the MBC is used with the HFB, 
the two systems could be connected (fig. 
35). 



30 



Miner operator 



Hopper feeder operator 



Miner- feeder 
cable handler 




<r ~l if Operator 



Two- pass 
continuous miner H °PP er feeder 



,nbyunlt Monorail track 



80 ' 

FIGURE 34. — Monorail bridge conveyor used with hopper-feeder. 



62" min 




take up 

FIGURE 35.— Monorail bridge conveyor-hopper-feeder interface. 



One operator is required for the entire 
MBC system, although it may be desirable 
to temporarily station a helper at the 
outby transfer point to the panel belt 
to assure proper transfer. Mine person- 
nel should be instructed to stay on the 
clearance side of the system where the 
emergency shutoff switches are located. 

In a continuous haulage mode with the 
MBC positioned directly behind the con- 
tinuous miner, the MBC operator would 
control tramming and steering to follow 
the miner. The pendant remote control 
will allow the operator to be positioned 
to avoid pinch points and to view loading 
operations. Various hopper capacities 
and profiles could be installed on the 
inby end of the system to maximize the 
target area for the miner operator. De- 
pending upon the mine plan, the miner 
power cable could be carried by the MBC. 

Two methods of monorail track installa- 
tion are possible. If lack of head room 
is a problem, the monorail track can be 



directly attached to the roof, using roof 
plates (fig. 25). Another method, using 
chain hangers, is shown in figure 24. 
Roof plates require two roof bolts for 
installation, while chain hangers require 
one. Chain hangers permit monorail in- 
stallation in high and uneven roof con- 
ditions. Figure 8 shows the two types 
of installation hardware. The size and 
length of the roof bolt would depend upon 
local mine conditions. Roof bolts that 
are part of the roof-control plan cannot 
be used for monorail suspension. Suspen- 
sion on 4-ft centers is recommended for 
straight track sections. Suspension on 
3-ft centers is recommended for curved 
track sections. 

Monorail track can be installed either 
on or off cycle with the cutting plan, 
depending on the mine and cut plan 
selected. Oncycle installation plans 
would require the roof-bolter crew to 
install monorail track in a cut immedi- 
ately after the cut Is bolted. Off-cycle 



31 




KEY 
■ Splice plate 

MK-5 monorail track designation; 
see figure 7. 

FIGURE 36.— Monorail track installation plan. 



installation plans would allow monorail- 
track installation during an idle shift. 
Monorail-track layout must be consistent 
with as-cut mine geometry to ensure ade- 
quate clearance at turnouts. Figure 36 



shows a typical track layout for 18-ft- 
wide entries and 60° crosscuts. The 
track should always be installed to main- 
tain clearance for personnel at all 
points on the right side of the MBC. 



CONCLUSIONS 



The MBC system, which includes the HF 
as a beneficial option, is a prototype 
continuous face haulage system that has 
the potential to significantly increase 
productivity and offer additional safety. 
Extensive surface tests were conducted 
by the Bureau to evaluate equipment per- 
formance criteria and to identify and 
make necessary modifications before con- 
ducting an underground trial. Successful 
test results under simulated mine condi- 
tions indicate that this innovative haul- 
age system offers the mining industry 



potential benefits for increased produc- 
tivity, while providing increased person- 
nel safety. Mining plans were developed 
that offer application of the MBC system 
for room-and-pillar, longwall develop- 
ment, and shortwall mining sections. A 
patent (U.S. Pat. 4,159,757) was granted 
to the Bureau in 1979 for the basic MBC 
concept. An in-mine trial is planned at 
a midwestern underground coal mine, using 
the MBC and HF as a continuous face haul- 
age system. 



32 



APPENDIX A.— MODIFICATIONS TO THE MONORAIL BRIDGE CONVEYOR SYSTEM 



Date 



Modifications 



Reason 



Sept. All interconnecting power and con- 
1982 trol cables between units were 
shortened. 



The original cables were too long and 
dropped onto the floor when connected. 
The extra weight also caused the conveyor 
units to lean toward the cables. 



Sept. New holes were drilled in the sus- 
1982 pension yokes to lower the inby 

attachment point of the units by 

2 in. 



Additional clearance was required at the 
transfer points between units so that 
spillage guards could be installed. 



Sept. Spillage guards were installed on 
1982 the inby end of each unit. Rub- 
ber belting was installed to pro- 
vide 6 in of overlap on each side 
of the 36-in-wide conveyor belt. 

Oct. Replaced pneumatic tires on the 
1982 inby tram drive with solid rubber 
tires. 



Preliminary loading trials revealed exces- 
sive spillage at the transfer points. 
The spillage guards also helped to center 
the coal on the conveyor belt. 



The original pneumatic tires required 
excessive steering effort (>50 ft* lb). 
Less than 20 ft* lb of effort was required 
with the solid tire. 



Nov. A steering motor, gearbox, and re- 
1982 mote steering-control circuit 

were installed for the inby tram 

drive. 

Nov. Isolation relays to provide in- 
1982 trinsically safe circuits were 

added to the tram and steering 

controls. 



The original manual steering was undesir- 
able because it was difficult to operate, 
and it put the operator in an unsafe 
position. 

Intrinsically safe circuits were required 
to enable use of nonexplosionproof limit 
switches and pendant control. 



Nov. Grease fittings were added to the 
1982 conveyor drive couplers. 

Nov. The spacing between the conveyor 
1982 return roller for the belt- 
sequence switch and the conveyor 
return roller for the belt-slip 
switch was increased from 24 to 
48 in. 



Additional lubrication was required to 
prevent frequent coupler disengagement. 

The original, closely spaced, return 
rollers were not turned by the belt dur- 
ing loading trials, because increased 
belt tension caused the belt to lift from 
the rollers. 



Nov. A 3/16-in/ft crown taper was added Belt-alignment problems were experienced 
1982 to the head and tail rollers. during coal loading trials. Crown taper 

tends to self-center the conveyor belt. 



Dec. Adjustable hoop-type angle deflec- 
1982 tors were added on the outby end 
of each unit. 



Deflectors were required to center the 
coal transfer to minimize spillage. The 
hoop-type deflectors were required to 
prevent coal from hitting the suspension 
yoke when two units were at an angle. 



33 



MODIFICATIONS TO THE MONORAIL BRIDGE CONVEYOR SYSTEM— Continued 



Date 



Modifications 



Reason 



Dec. 
1982 



Jan. 
1983 



The profile of the suspension yoke The original suspension yoke was struck by 
was modified to allow a greater coal when units were at their raaxiraum- 
opening for coal transfer. angle relationship. 



Compression-spring-type belt 
cleaners were installed under- 
neath the head roller. 



Belt cleaners were required because coal 
tended to accumulate on the underside of 
the conveyor belting, causing belt mis- 
alignment and opening of the slip switch. 



Jan. A lightweight pendant control was 
1983 installed. 



June The wheel base between the 9-in- 
1983 wide inby rubber tires was in- 
creased from 12-in centers to 
38-in centers. 



Originally, an explosionproof control unit 
was installed. This heavy unit was awk- 
ward to use and only had controls for 
conveying and tramming. Extra controls 
were required because a steering motor 
was previously added. 

Tramming tests proved that the inby unit 
was unstable with original close-wheel 
base. Stability is required to prevent 
belt misalignment. 



June The inby tram drive was changed to 
1983 a gear-speed reducer mounted be- 
tween the inby rubber tires. 

June Limit switches were installed to 
1983 limit the allowable steering arc 
of the inby wheel carriage. 



The original chain and sprocket drive was 
unreliable and had poor ground clearance. 



Without limit switches, the wheel carriage 
turned until stopped by mechanical inter- 
ference. This in turn would overload the 
steering motor. 



June A limit switch was installed to 

1983 detect when the inby monorail 
carrier reached the end of the 
monorail track. 

Aug. A heavier inby tram-motor torque 

1984 arm was anchored to both sides of 
the through-bolts on the inby 
tram-speed reducer. 

Aug. Cast bearings were installed to 
1984 support the steering shaft. 



This switch prevents the monorail carrier 
from tramming off the inby end of the 
monorail track, thereby avoiding a possi- 
ble safety hazard and operational delay. 

The original torque arm was only attached 
to one side of the speed reducer, and it 
failed during tramming tests. 



The original pressed bearings did not 
resist the lateral thrust produced by 
the steering shaft. This caused the 
steering-shaft key to disengage from the 
drive coupler. 



Nov. The inby tram drive was changed 
1984 from two- to one-wheel drive. 



The original design with both wheels 
mounted on a solid shaft required exces- 
sive torque requirements for steering, 
since the wheels would slide instead of 
roll during steering maneuvers. 



34 



MODIFICATIONS TO THE MONORAIL BRIDGE CONVEYOR SYSTEM — Continued 



Date 

Nov. 
1984 



Dec. 
1984 



Feb. 
1985 



Modifications 

A brake was added to tbe steering 
motor. 



Reason 

The brake was required to lock the steer- 
ing carriage when the steering motor was 
not in operation. 



A new explosionproof steering con- The control box was required for steering 

trol box was installed on the controls, 
inby unit. 

A 5/16-in-thick MSHA-approved PVC The original, 3/16-in-thick belt was not 

conveyor belting was installed in adequate for underground use. 
all units. 



Feb. 
1985 



Feb. 
1985 



Several 4-in-diam clearance holes 
were burned into the conveyor 
frame to allow better access to 
the conveyor drive coupler. 



The original 1.5-in-diara hole made coupler 
adjustment difficult. 



Gussets were added to the sides of The switch mounting frames would be prone 
the sequence and slip-switch to damage during MBC installation because 
mounting frame. they extended below the main conveyor 

frame. 



Mar. The 480-V ac to 120-V ac trans- 
1985 formers were installed into each 

motor control box to power system 

controls. 



Mar. Isolation relays to provide in- 
1985 trinsically safe sequence-switch 

circuits were installed into each 

control box. 



Modification was required to meet MSHA re- 
quirements. Originally, 120-V ac control 
power for all units was supplied by one 
transformer in the master control box; 
however, this 120-V ac power was inter- 
mingled with intrinsically safe control 
wiring in a multiconductor cable. 

Modification was required to meet MSHA 
requirements. Previously, the 120-V ac 
sequence-switch circuits were inter- 
mingled in the multiconductor cable with 
intrinsically safe circuits. 



Mar. The brake overhead indicator lamps These items were removed to provide space 
1985 and associated relays were re- for the transformer and isolation relays 

moved from each motor control 

box. 



Mar. A 480-V ac to 120-V ac and 12-V ac The 120-V ac power was required for steer- 
1985 dual secondary transformer was ing control, and 12-V ac power was re- 
added to the steering control quired for lighting, 
box. 



35 



Date 



MODIFICATIONS TO THE MONORAIL BRIDGE CONVEYOR SYSTEM— Continued 
Modifications Reason 



Mar. A main circuit breaker explosion- 
1985 proof control box was added to 
the MBC control system. 



Modification was required to meet MSHA re- 
quirements. Previously, the contactor in 
the master control was the main circuit- 
interrupting device; however, with the 
contactor, there was 120-V ac power in 
all units, even when the main power 
switch was in the "off" position. 

A new main breaker box was required be- 
cause the existing master control box 
did not have an opening for a circuit- 
breaker reset handle. 



Mar. Fuses were removed from the line 
1985 side of the 480-V ac transformer 
in the master control box. 



If the fuses were left in, the master con- 
trol box would require a panel-interlock 
switch. 



Mar. The ground-monitor circuit was 
1985 removed from the master control 
box. 



The circuit would be redundant with the 
load-center ground-monitor circuit. 



Mar. An explosionproof junction box was 
1985 added on the inby unit so that 
both headlights could receive 
power from one cable exiting the 
steering control box. 

Mar. An explosionproof junction box was 
1985 added to the outby unit so that 
both taillights could receive 
power from one cable exiting the 
master control. 



An extra cable-entrance gland was required 
in the steering control box for the 
steering control brake. 



An extra cable-entrance gland was required 
in the master control box for the main- 
breaker shunt-trip cable. 



Apr. All interconnecting cables were 
1985 placed in MSHA-approved flame- 
resistant hose conduit. 



Modification was required to meet MSHA 
requirements. 



June New cable hangers were installed 
1985 on all units. The new cable han- 
gers acted as trays and could 
hold several cables. 



Previously, separate cable hangers were 
installed for each interconnecting cable. 
This made adjustments awkward. 



June Tapped mounting bosses were in- 
1985 stalled on the inby end of each 
unit. 



The mountings were required to permit 
rapid attachment of a changeout bracket. 
The bracket is connected to a monorail- 
suspended chain hoist when unit changeout 
is required. 



688 365 



U.S. GOVERNMENT PRINTING OFFICE: 1987 605-01 7'60 070 



INT.-BU.OF MINES,PGH.,PA. 28526 



U.S. Department of the Interior 
Bureau of Mines— Prod, end Distr. 
Cochrane Mill Roed 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



OFFICIALflUSINESS 
PENALTY FOR PRIVATE USt MOO 



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